GM: update readme, ACC is a required package (#354)
GM: update readme, ACC is a required package (#354)

ACC implies Driver Confidence II, but not the other
way around. Openpilot requires front, long range radar
that only comes with ACC package.
vntarasov/openpilot,vntarasov/openpilot,vntarasov/openpilot,vntarasov/openpilot